1. Field of the Invention
The present invention relates to an image display device.
2. Description of the Related Art
Image display devices called head up displays are known. Head up displays have an optical element called combiner. This combiner allows external light to pass through and reflects image display light projected from an optical unit provided in a head up display. This allows the user to visually recognize an image related to the image display light while overlapping the image on a landscape via the combiner.
These image display devices called head up displays have received attention as in-vehicle image display devices in recent years since the image display devices allow a driver of a vehicle to also recognize, almost without changing the direction of the line of sight or a focus for visually recognizing a view outside the vehicle, information of an image projected from an optical unit.
For example, Patent document No. 1 discloses a head up display to be mounted on a dashboard of a vehicle that adjusts, by using an X-axis stage, a Z-axis stage, and a rotation stage, a space that can be visually recognized by a user.
[Patent document No. 1] Japanese Patent Application Publication No. 10-278629
Head up displays such as those described above display an image related to image display light while overlapping the image on a landscape via a combiner. Thus, when the head up displays are used under an environment illuminated by external light, the contrast of the image display light is relatively lowered in comparison with that of the external light, and the user's visibility may be affected thereby.